Field of the Invention
The present invention relates to a light scanning apparatus and an image forming apparatus, and more particularly, to a light scanning apparatus to be arranged in an electrophotographic image forming apparatus such as a digital copying machine, a laser beam printer, and a facsimile machine.
Description of the Related Art
A light scanning apparatus to be arranged in an image forming apparatus is configured to form a light spot, which is obtained by converging laser light emitted from a semiconductor laser through an optical element such as a collimator lens and an fθ lens, on a surface of a photosensitive drum which is a scanned surface. The light scanning apparatus includes a deflector such as a rotary polygon mirror configured to deflect the laser light emitted from the semiconductor laser. A desired electrostatic latent image is formed on the surface of the photosensitive drum by scanning the surface of the photosensitive drum with the laser light deflected by the deflector while repeating light emission and stop of the light emission from the semiconductor laser. Through an electric cable, power is supplied to the deflector and operation instruction signals for the rotary polygon mirror are transmitted to and received from the deflector. The electric cable passes through a hole portion or a cut-away portion formed in a casing of the light scanning apparatus or a cover member which is mounted so as to cover an opening portion of the casing, and the electric cable is connected to a control board arranged outside of the light scanning apparatus.
The electric cable passes through the hole portion or the cut-away portion which is the opening portion formed in the casing or the cover member. Therefore, outside air containing dust or dirt is sucked into the light scanning apparatus through the opening portion. Therefore, the dust or dirt contained in the sucked outside air adheres to reflecting surfaces of the rotary polygon mirror or a reflecting surface of a reflecting mirror to contaminate the surfaces thereof. Further, the contamination of a part of the reflecting surface configured to reflect the laser light changes a light quantity of the laser light that successfully reaches the surface of the photosensitive drum which is the scanned surface. Therefore, density unevenness is caused in an output image formed on a sheet to degrade image quality.
The opening portion through which the electric cable is laid is generally formed as small as possible, and therefore the amount of outside air entering the light scanning apparatus through the opening portion is extremely small. However, due to the adhesion of the dust or dirt contained in the outside air onto the reflecting surfaces of the rotary polygon mirror or the reflecting surface of the reflecting mirror, the amount of reflected laser light changes. As a result, because an image which is formed through electrophotography generally reacts sensitively to the change in light amount, the inflow of the outside air through the opening portion cannot be ignored.
Further, in recent years, the light scanning apparatus operates at a higher speed. Therefore, the number of rotations of the rotary polygon mirror is increased to increase a rate of airflow generated around the rotary polygon mirror. As a result, there are generated a positive-pressure portion and a negative-pressure portion inside the light scanning apparatus to increase a suction force for sucking the outside air from outside to inside of the apparatus. Thus, a larger amount of outside air is disadvantageously sucked even through the extremely small opening than before. As described above, due to the contamination of the reflecting surface of the optical component, maintenance work such as replacement of the light scanning apparatus and cleaning of the reflecting surfaces of the rotary polygon mirror increases. Therefore, in order to deal with the above-mentioned problem, the following countermeasure has been taken. Specifically, a soft sealing member such as a foamed member is fitted into the opening portion through which the above-mentioned electric cable passes. For example, in Japanese Patent Application Laid-Open No. H09-26553, a portion of an outer peripheral wall of a casing of a deflection scanning apparatus, through which the electric cable passes, is filled with a foamed member such as Moltoprene so as to prevent the outside air containing dust or dirt from entering the apparatus.
However, cells of the foamed member are continuously linked although linked portions are extremely small. Therefore, the outside air undesirably enters the apparatus through the cells of the foamed member. Therefore, the reflecting surface of the optical component is contaminated with the dust or dirt contained in the entering outside air. Thus, there arises a problem in that satisfactory image forming performance cannot be obtained. Further, for filling of the foamed member, work must be carried out while confirming whether or not the foamed member reliably covers the periphery of the electric cable, resulting in low workability. Further, the foamed member is soft, and therefore, if a shape of the foamed member is warped due to a sliding resistance between the electric cable and the foamed member when the electric cable and the foamed member are accommodated in the cut-away portion of the casing, a clearance is generated. Thus, there also arises a problem in that intended dustproof performance cannot be obtained.